1. Field of the Invention
The present invention relates to a Si/C superlattice useful for semi-conductor devices, in which layers of epitaxial silicon alternate with layers of adsorbed carbon. The invention also relates to structures useful for electronic or opto-electronic devices comprising the superlattice. Such devices include transistors such as field effect transistors, MOSFET's, power transistors, quantum well devices, and light emitting devices.
2. Description of the Related Art
Electronic and opto-electronic devices incorporating superlattices are described, e.g., in U.S. Pat. No. 6,294,802 issued to Unozawa; No. U.S. Pat. No. 6,355,951 issued to Hattori; U.S. Pat. No. 6,479,836 issued to Suzuki et al.; and U.S. Pat. No. 6,452,206 issued to Harman et al.; the disclosure of each of said U.S. patents being incorporated herein by reference.
The production and properties of silicon carbide materials and Si/O superlattices (having alternating silicon and adsorbed oxygen layers) are disclosed in the following publications, which will be referred to below:                1. Silicon Carbide and Related Materials-1999, Oct. 10–15, 1999, ICSCRM'99 Edited by C. H. Carter, Robert P. Devaty and G. S. Rohrer, Trans Tech Publishing, 2000.        2. R. Tsu, A. Filios, J. Lofgren, J. L. Ding, Q. Zhang, J. Morais, and C. G. Wang, Electrochem Soc. Proc. 97–11, 341 (1997).        3. J. Ding and R. Tsu, Appl. Phys. Lett. 71, 2124 (1997).        4. R. Tsu “Si Based Green ELD: Si-Oxygen Superlattice, Phys. Stat. Sol. (a) 180, 333 (2000).        5. D. Morelli, J. Hermans, C. Beetz, W. S. Woo, G. L. Harris and C. Taylor, Inst. Phys. Conf. Ser (UK) 137, 313 (1993).        6. R. Tsu, K. Dovidenko and J. C. Lofgren, Electrochem Soc. Proc. 99–22, 294 (1999).        7. Y. J. Seo and R. Tsu, Jpn J. Appl. Phys. 40, 4799–4801 (2001).        8. Y. J. Seo, J. C. Lofgren and R. Tsu, Appl. Phys. Lett. 79, 788 (2001).        9. U. Gosele “Semiconductor Wafer Bonding” Ann. Rev. Mat. Sci. 28, 215 (1998).        
U.S. Pat. No. 6,376,337 issued to Wang et al., and co-pending U.S. Ser. No. 09/617,511 filed Jul. 14, 2000 disclose epitaxial silicon on insulator structures and devices employing a Si/O superlattice.
Silicon carbide power devices have been considered over the years in high power and high temperature environments primarily for their larger bandgap enabling operation at temperatures beyond 300° C., and high thermal conductivity for high power operations. This goal has not been fully realized due mainly to the material defects and the packaging limitations of the devices. At present, silicon carbide wafers are produced mostly at two inch diameter with poor quality. Defects such as micropipes, stacking faults, and dislocations remain quite high on relatively small diameter wafers [see 1 above]. On the other hand, the Si/O superlattice with epitaxially grown silicon layers sandwiched between adsorbed monolayers of oxygen has very low defect density and an effective bandgap much higher than silicon [2,3,4 above]. Such a structure shows two attractive novel functions: the superlattice region can serve as an insulating material allowing the fabrication of epitaxial silicon beyond the insulating superlattice region; and electro- or photo-luminescence in the visible spectrum to be used for possible opto-electronic operations.
The room temperature thermal conductivity of 3C (3-cubic crystal form) SiC is more than three times that of silicon [5 above], and even higher for 6H (6-hexagonal crystal form) SiC. On the other hand, silicon thermal conductivity is higher than SiO2 by an order of magnitude. Without knowing the fundamental reasons for the high thermal conductivity of SiC at present, the trend indicates that the thermal conductivity of the Si/C superlattice will be higher than silicon. Therefore the possibility of fabricating an epitaxially grown low defect Si/C superlattice from a silicon template with an effective bandgap of well over 2 eV and improved thermal conductivity over silicon, indeed offers an ideal material for high temperature electronics. The new Si/C performance characteristics are expected to be superior to silicon carbide currently fabricated by CVD (Chemical Vapor Deposition) under a very high thermal budget, or even superior to GaN materials presently being developed.